FIG. 8 is a partial cross-sectional view of prior art camshaft phaser 200 showing contaminated oil migration. FIG. 9 is a plan view of the check valve plate in FIG. 8. The following should be viewed in light of FIGS. 8 and 9. Camshaft phaser 200 includes: stator 202; rotor 204 located radially inward of stator 202; at least one chamber 206 bounded at least in part by stator 202 and rotor 204; locking cover 208; spring cover 210 non-rotatably connected to locking cover 208; space 212 enclosed, at least in part, by spring cover 210 and locking cover 208; channel 214 in cover 208; spiral spring 216 located in space 212, and check valve plate 218. Fluid 220, for example oil from an engine (not shown) including phaser 200, is present in space 212.
As is known in the art, fluid 220 flows into and out of chambers 206 to establish a rotational position of rotor 204 with respect to stator 202. For example, when fluid pressure in space 212 is greater than fluid pressure in chambers 206: fluid 220 displaces flaps 224 of plate 218 (covering channels 214) in axial direction AD1; and fluid 220 flows through channels 214 along path 222 into chambers 206. For example, when fluid pressure in space 212 is less than fluid pressure in chambers 206, fluid 220 in chambers 206 displaces flaps 224 in axial direction AD2 to block fluid flow out of chambers 206 and into space 212 through channels 214.
Fluid 220 typically becomes contaminated by magnetic and non-magnetic particulate generated by operation of the engine. In general, contamination degrades the phasing function of phaser 200. For example, the contaminant can interfere with operation of the check valve plate (for example preventing flaps 224 from properly opening or blocking channels 214). Interfering with operation of the check valve plate degrades operation of phaser 200, for example by preventing proper operation of the engine timing operations dependent upon the proper transport of fluid into and out of chambers 206.